Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft drives the generator rotor either directly (“directly driven”) or through the use of a gearbox. The operation of the generator produces the electricity to be supplied into the electrical grid.
Wind turbines normally comprise pitch systems that are employed for adapting the position of the blades to varying wind conditions by rotating each blade along its longitudinal axis. This adaptation of the position of the blades is used to adjust the operation of the wind turbine. in terms of e.g. reducing or even stopping rotation of the rotor.
Wind turbines are often grouped together in so-called wind farms. In a wind farm there may be a relatively short distance between wind turbines. Thus, action of the wind on one wind turbine may produce a wake which may be received by another wind turbine. A wake received by a wind turbine may cause high loads (particularly vibrations) and/or a reduction of electrical power production in this wind turbine. These high loads may damage components of the wind turbine, and these damages may reduce the life and/or the performance of the wind turbine. Therefore, wakes in a wind farm should be avoided as much as possible.
Currently, it is known that some wake management strategies are defined by simulating loads for a theoretical layout and wind conditions. For every wind turbine in the layout, a set of adjustments in the operation of the wind turbine (e.g. stops) is defined for determined wind directions so that simulated loads will not theoretically result in damage for the wind turbine. These adjustments are entered in a control system (e.g. a SCADA control system) which applies them in the wind farm by e.g. sending suitable signals to e.g. the corresponding pitch systems, brakes, etc. The application of such adjustments in the operation of wind turbines is supposed to reduce loads in the wind farm.
Nevertheless, this known application of strategies may present many problems, mainly because it is complicated to measure wind conditions and because, even if the wind is measured with high accuracy, significant uncertainty may arise from the model used to estimate loads from the acquired wind data. For example, measurement of the wind direction may fail and thus the whole strategy may be poorly implemented. The detection of this kind of failures is complicated because it does not lead to immediate error, but to fatigue which may produce noticeable consequences only after a long time.
Besides, the measurements of wind speed are usually not performed in the affected machine because, when it is in a wake of a neighbouring wind turbine, all the measurements may be spoiled and of no use. This is the reason why the value of wind speed and direction for which the wake management strategy (e.g. an interruption) is defined is usually measured somewhere else in the site (e.g. in another wind turbine or a met mast which are not affected by a wake). This may lead to incorrect application of the wake management strategy because there could be differences in the wind measured by the reference wind turbine/met mast, and the wind actually affecting the wind turbine of study.
Another problem is that this type of strategies does not respond to changing needs due to changes in the external conditions such as construction of a neighbouring wind farm, variations in the forestry areas, etc. Said external conditions may generate wakes which have not been considered in the simulation of loads. Besides, certain deviations may exist between pre-defined wind turbine locations and the actual ones, so that the actual wind farm layout after installation can differ from the theoretical layout that is used in the initial simulations. These deviations may be significant or not.
In addition, if the input wind distribution used in the study does not correspond to the real wind distribution (both in wind speed and wind direction) then the pre-defined strategy might be useless or even prejudicial for the wind turbine loading and for total wind farm power output.
Furthermore, some layout conditions such as height differences between the wind turbines are usually not taken into account in the current definition of the wake management strategy. In some cases, this may lead to more adjustments in the operation of wind turbines than actually needed. The total production of electricity of the wind farm may thus be negatively affected.
Also, current wake models might not be accounting properly for the influence of “partial wake situations” leading to risky situations if this partial wakes happen often enough in a given layout.